This invention relates generally to suspension mountings, and more particularly, to mountings for the steering system of a railway truck.
Mountings with load suspension and vibration-dampening capabilities have been used in the past to improve the steering and ride characteristics of railway trucks. A typical railway truck includes two side frames connecting front and rear wheelsets mounted on axles. The side frames are connected by a cross-member or bolster and provide the railway truck with a stiff structure for mounting a railway car for carrying cargo. An elastomeric mounting, which is a mounting that includes a pad of an elastic material like rubber or another elastomeric material, is typically positioned between an axle bearing adapter and the side frame adjacent to each wheel to support the frame and car on the axle. The elastomeric mountings permit the axles of the railway car to move horizontally with respect to the side frames to allow the axles to turn or follow the rail curvature. Additionally, the elastomeric mountings support vertical static and dynamic loads, such as the weight of the frame and cargo in the car. This type of suspension is typically utilized in, for example, radial self-steering and non-radial railway trucks. By allowing the axles to turn with respect to the railway truck, the elastomeric mountings reduce the friction between the wheels and the rail, thereby improving their life. Additionally, the reduced friction makes the railway truck easier to pull, thereby increasing fuel economy for the train locomotive.
The railway truck may experience ride control problems when using typical elastomeric mountings, however, due to the mountings' lack of control over lateral horizontal motion independent of longitudinal horizontal motion. For example, lateral motion of the axles with respect to the side frames can contribute to instability of the railway truck at high speeds, which produces poor ride characteristics. Since the elastomeric pad of a typical elastomeric mounting is generally flat in the horizontal plane, the lateral spring rate typically is about equal to the longitudinal spring rate. As such, it is generally not desirable to increase the lateral spring rate of the flat elastomeric pad, because this will result in the longitudinal spring rate being correspondingly increased, negatively affecting the steering characteristics of the railway truck.
In order to increase the lateral spring rate independent of the longitudinal spring rate, some elastomeric mountings have included alternating layers of elastomeric pads and rigid shims having a V-shaped, or inverted V-shaped, cross-section. The V-shaped cross-section is in a plane parallel to the axles, or perpendicular to the side frames. For instance, one such elastomeric mounting is described in U.S. Pat. No. 3,699,897 to Sherrick, issued Oct. 24, 1972 and assigned to the assignee of the present invention. The V-shaped cross-section provides a laterally-inclined surface that increases the lateral spring rate of the mount, but does not affect the longitudinal spring rate. Also, the V-shape of the rigid shim, for example, serves to contain the lateral movement of the elastomeric pad, reducing the amount of pure shear and increasing lateral compression within the elastomeric pad, thereby increasing the lateral spring rate. Similar mounts have used other curved cross-sectional shapes, as well as flanges, to restrain the lateral motion of the mount.
These solutions have had limited success in increasing the lateral spring rate, however, because the angle of the inclined V-shaped cross-section is limited by the allowed space for the mount. In many cases, elastomeric mountings are required to adapt to, improve or be retrofit into existing railway trucks. As a result, the available space for the mount may be limited to the space occupied by the existing mount. This available space generally cannot be increased, for example, due to railway truck height limitations for going under bridges and through tunnels, and due to coupler height limitations to permit adjacent railway trucks to be coupled together. In many cases, this available space does not allow a sufficiently inclined V-shaped section to provide a desired lateral spring rate. Thus, since the spring rate of the elastomeric pad cannot be increased without unwelcome changes to the longitudinal spring rate, a less than optimal solution is provided by mountings having V-shaped or other curved-shaped cross-sections.